WASHINGTON - As member of the House Natural Resources Committee and a former oil-industry executive, U.S. Rep. Bill Flores of Bryan is at the center of big debates about offshore drilling, hydraulic fracturing and domestic energy supplies.

According to Flores' most recent financial-disclosure filings with the House of Representatives, the Texas Republican spent at least $1.6 million - and possibly as much as $3.25 million - buying energy-related stocks during the first half of November. Among his pickups: Tesoro Logistics, the master limited partnership formed by San Antonio-based refiner Tesoro Corp. in 2011; and Tulsa-based Williams Companies.

During the same time frame, Flores also collected as much as $1.4 million from selling energy stocks, including Linn Energy, Crestwood Midstream Partners and NGL Energy Partners. He had previously purchased $250,001 to $500,000 in Linn Energy stock on Oct. 25 and as much as $250,000 in Crestwood stock on Oct. 18.

The Capitol Hill newspaper Roll Call first reported the transactions.

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No congressional ethics rules widely bar lawmakers from taking official action that affects entities in which they have financial interests - unless they would be affected uniquely. That means, for instance, that lawmakers who hold pharmaceutical stocks in their financial portfolios are free to cast votes on health care bills and even introduce such legislation.

In Flores' case, it means he was able to introduce legislation in July that would change rules for taxing natural gas pipeline property, sign on to a bill that would do away with federal renewable fuel mandates and sponsor legislation that effectively would block new Interior Department rules governing hydraulic fracturing on public lands.

Robert Walker, a former counsel to the House and Senate ethics committees who now is in private practice at Wiley Rein, notes that lawmakers also are not barred from trading in securities unless they would be acting with material, non-public information - the same insider trading prohibition that applies to other investors.

Flores said that an independent third-party manages his financial portfolio, often making trades well before the lawmaker is notified about them. For instance, Flores reported that he shed as much as $500,000 in Kinder Morgan stock on Oct. 25 but first learned of the transaction when he received a statement on Dec. 9. The transaction was reported in Flores' filing with the House of Representatives a day later.

"There has been no conflict of interest between my service in Congress and the management of my investment portfolio by an independent, third-party portfolio manager," Flores said. "This portfolio manager executes trades based upon a pre-established portfolio allocation and a formula-driven income generation strategy (that) has included an active energy MLP trading component since January 2009."

Flores said many of the short-term trades in master limited partnerships are based upon the quarterly cash distribution schedules of the companies he holds.

A handful of lawmakers have opted to put financial holdings in blind trusts to avoid the appearance that they are profiting from legislative dealmaking.

But Walker notes that these are individual judgment calls for lawmakers.

"By their very nature, such appearance calls are for individual members to make - and to live with - as they judge best," he said.

"While it's not strictly prohibited, members are still supposed to avoid even the appearance of impropriety," said Melanie Sloan, the executive director of the not-for-profit Citizens for Responsibility and Ethics in Washington. "Given how much concern there is about members using their position to profit, this is the kind of activity … that feeds public skepticism about Congress."

Lawmakers are required to file regular disclosures on their financial transactions, under a 2012 law called the "Stop Trading on Congressional Knowledge" Act. Previously, they only had to file annual disclosures that shed some light on their holdings.

But even the more frequent disclosures only crack the door a bit, because lawmakers can report stock sales, purchases or exchanges under widely varying categories of value, such as $250,001-$500,000 or "over $50 million."

The revelations may feed concerns about insider trading, if only because lawmakers and congressional aides may get non-public data during their work. Lawmakers who sell assets to avoid the appearance of impropriety during a congressional investigation or talk with federal regulators may open themselves up to insider-trading accusations.